1. Field of the Invention
The present invention relates to a bumper system for a vehicle excellent in load energy absorbing performance at the time of a vehicle collision, particularly excellent in characteristics mitigating the impact applied to a human body and reducing the damage to a pedestrian at the time of the collision with the pedestrian.
2. Description of the Related Art
On the vehicle body of automobiles and the like, a bumper system reducing the impact load by deforming in the direction of the collision and absorbing the impact energy for ensuring the safety of an occupant and protecting a collided pedestrian's body at the time of the vehicle collision is known.
A representative example of the bumper system is the one constituted of a bumper beam of iron and steel or of an aluminum alloy mounted at the front face of bumper stays, a cushioning material of foamed resin arranged in front of it, and further in front of which, a bumper cover often formed integrally with outer face of the vehicle.
Recently, to achieve the weight reduction of a vehicle, an aluminum alloy extruded hollow shape or the like has begun to be in use for these bumper beams instead of steel. The aluminum alloy bumper beam is formed of a hollow material with the section of a variety of generally rectangular shape extending in the width direction and with an appropriate bend to match the vehicle body external shape. For the iron and steel bumper beam, configuration is almost same with the exception that the hollow material is often an open sectional member.
For these vehicle body bumper systems, functions are required for reducing the impact load and absorbing the impact energy at the time of collision from the front side or the rear side of the vehicle or the collision of the vehicle to the front side or the rear side by the bumper beam supported by the vehicle body and the cushioning material of a foamed material arranged in front of it.
With respect to these impact energy absorbing functions, the protection of the pedestrian at the time of a collision with the pedestrian has also been newly required in addition to collision with a “highly rigid object” such as a vehicle or other objects (guard rail, pole and the like).
For example, the representative examples of the damage to the pedestrian at the time of the collision of the vehicle against the pedestrian are a head, a waist and a leg part, and the European Enhanced Vehicle-safety Committee and etc. are conducting a New Car Assessment Program (NCAP). According to it, a pedestrian protection characteristics assessment test is proposed for each of the head, the waist and the leg part, which is becoming a standard assessment method for protection of the pedestrian by the vehicle. Among these assessment tests, the assessment test method on the leg part, which is the part the bumper system relates to, stipulates a test in which the leg impactor imitating the leg of the pedestrian is made to collide with the bumper system at the speed of 40 km/h. At the time of the collision, the output of various type of sensors (acceleration, shearing deformation quantity, bending angle) provided in the leg impactor is required to be equal to or less than a prescribed value. In particular, the acceleration value should be 150 G or less.
However, the bumper systems disclosed until now were devised under an assumption of the collision with a “highly rigid object” such as a vehicle or other objects (guard rail, pole and the like), therefore most of them were designed under an assumption of the collision with objects of comparatively high rigidity and high strength. Accordingly, with these bumper systems, acceleration, particularly, surpasses the restriction value among the assessment values (acceleration, shearing deformation amount, bending angle) at the time of the collision with the leg model of the pedestrian.
On the contrary, in the bumper systems designed with lowered strength and rigidity in order to protect pedestrians, the functions of reducing the impact load and absorbing the impact energy at the time of collision with the pedestrian's body causes high rigidity and high strength to be deteriorated. As such, the bumper system is required to compatibly satisfy these conflicting functions.
In this regard, although a variety of ideas such as arranging an impact absorbing device or an air bag in front of the bumper beam (bumper reinforcement) are conventionally proposed, they are not yet put to practical use. Therefore, usually (practically), measures of arranging a comparatively thick absorber (cushioning material, an energy absorbing member) such as a urethane foam material or styrene foam material in the location front of the bumper beam and back of the bumper cover have been taken. However, in designing a vehicle body, there is a limit in the thickness of the absorber arranged, and there actually is a limit in the pedestrian protecting performance (impact energy absorbing function) as well.
On the other hand, in addition to the absorber described above, the bumper beam with an impact buffer member for vehicle collision arranged in the front is conventionally proposed. In such a bumper system, the impact buffer member is deformed in the direction of the thickness of the section (cross-sectional direction) at the time of the collision of the vehicle and the impact of the vehicle collision is buffered. With this configuration, the bumper reinforcement material newly adding the function of pedestrian protection can be provided without deteriorating the function of high rigidity and high strength which is the original function of the bumper beam (bumper reinforcement).
For example, in Japanese Unexamined Patent Application Publication (JP-A) No. 2004-114864, an impact buffer member of a hollow structure having an abutment wall positioned apart from the outer end face of a bumper beam by a prescribed distance to receive an impact from the collided pedestrian's body at the time of collision, and support walls extended from installation walls abutted on the bumper beam to support the abutment wall from the back side is proposed. Each of the support walls is constituted to comprise a curved support wall along the installation wall to be curved and extended in a range of a prescribed width continuous with the installation wall. When impact is applied to the abutment wall through the object, the curved support walls are deformed in their curvature direction to be bent.
In JP-A-2003-285704, an impact reduction vehicle bumper system for a vehicle having at least two frame rails mounted on the vehicle body, at least two brackets coupled respectively to the frame rails, a beam attached to the brackets, a plate member attached to the beam, and frame rail extensions coupled to the brackets is proposed.
In JP-A-2003-312397, an energy absorbing member for personal protection is proposed, wherein a shape of bellows-shape is extended in the direction such that the direction of the bellows-shape becomes in parallel with the load of collision from the front, the bellows-shape is deformed at the time of the collision with a pedestrian, and the maximum load during the loaded displacement is decreased, thereby securing the energy absorption amount required for protection of a pedestrian.
In JP-A-2004-90910, an energy absorbing member for personal protection is proposed which consists of a front flange and a rear flange provided approximately in parallel in the longitudinal direction of the vehicle and right and left webs provided approximately in parallel and connecting between these flanges, the respective web consisting of an aluminum alloy hollow shape curved toward outside respectively. With this configuration, at the time of collision with a pedestrian, the respective web is deformed, the entire member is gradually deformed into a flat shape just like the open/close motion of a pantograph of an electric train, the maximum load during the loaded displacement is decreased, and the energy absorption amount required for protection of a pedestrian can be secured.
However, in JP-A-2004-114864, because the impact buffer member is a hollow member made of resin, in order to get enough performance for protecting the pedestrian's leg, the thickness needs to be considerably thick compared with the cushioning material made of a metal, and lightening is sacrificed. Also, in its production, the material and the thickness of resin are restricted and the problem of inferior recycling property compared to the cushioning material made of a metal is involved.
On the other hand, in designing a vehicle body or in the case of a small sized vehicle, the distance (clearance) between the face of the bumper beam (bumper reinforcement) in the side of the vehicle front and the bumper cover becomes narrower, therefore the width of the impact buffer member (energy absorbing member for personal protection) in the longitudinal direction of the vehicle must be made narrower. In this regard, in the impact buffer member as described in JP-A-2003-285704, the length of the plate member in the longitudinal direction of the vehicle becomes comparatively long (the plate member protrudes long in front of the bumper beam) in order to secure the energy absorption amount required for protection of a pedestrian, therefore it cannot be applied to some vehicle designs (vehicle kinds).
Furthermore, in the actual collision, the collision position of a pedestrian differs respectively. Accordingly, it may possibly happen that the collision position of a pedestrian largely shifts from the position where the energy absorbing member is installed. They are, the case where the collision position of a pedestrian's leg is shifted in the direction of vehicle width, the case where the collision direction of a pedestrian leg is shifted in the horizontal direction, or the like. In order to generate the desirable displacement of the cushioning member (energy absorbing member) to cope with these cases, the energy absorbing member for personal protection with a comparatively large area extending over the front face of the bumper reinforcement is required.
When the area of the cushioning member is comparatively enlarged as described above, the weight of the cushioning member constituted in a comparatively thick wall thickness as described in JP-A-2003-312397 and JP-A-2004-90910 is increased and lightening is sacrificed. Also, if the case that the collision direction of a pedestrian's leg is shifted with respect to the up-down direction of the vehicle (vertical direction) is considered, this means a shift of the line of action of the compressing force, in such a cushioning member utilizing the collapse of the shape toward the direction of the thickness of the section. In the cushioning member utilizing the collapse to the direction of the thickness of the section, if the line of action of the compressing force is shifted, the energy absorbing performance becomes liable to be deteriorated. As such, in this type of cushioning member, the thickness of the section is forcibly increased by the shift of the collision position of a pedestrian as well, in order to retain the energy absorbing performance. From this viewpoint, in such a cushioning member, the energy absorption amount required for protection of a pedestrian is hard to be secured.